"I have a family room over my garage that was finished with interlocking
knotty pine planks.........................I would like to change from
that look to something brighter, but don't want to tear out all the
planking........it appears that it was finished with a shellac..........as
it is a dull reddish yellow and has dried out pretty
much....................I thought maybe some translucent white might be
nice as I would like to use the pine characteristic's but I am afraid
anything light will end up a mess if the old finish bleeds through
......ay one been through this or have a solution???????????

Won't be long before knotty pine will come back in style like gang busters.
Don't be too quick to paint it. A good cleaning/sanding/reshellacing may
make it much brighter. If you must paint it, shellac can be a stain
blocker, but if it is old, the knots may still bleed their pitch thru to the
surface of the new paint. To seal it for sure, use zinsser or other such
stainblocker, then paint with opaque paint, but this approach will obscure
all traces of the knots , which you apparently don't want.There also may be
a way to bleach the surface with chorox, before refinishing - we have done
this before, with good lightening effect. You might also get opinion of
expert painter that deals in faux finishes and various washes.